Substrate for suspension, and production process thereof

ABSTRACT

A substrate for suspension which is produced at low costs and can sufficiently attain the prevention of damage by electrostatic discharge and restraint of noises. The substrate for suspension includes: a metallic substrate, an insulating layer formed on the metallic substrate and having an opening from which the metallic substrate is exposed, a grounding-wiring layer formed on the insulating layer and arranged near the opening, and a ground terminal formed in the opening and contacting the metallic substrate and the grounding-wiring layer. The ground terminal is made of a metal having a melting point of 450° C. or lower.

TECHNICAL FIELD

The present invention relates to a substrate for suspension which isproduced at low costs, and can sufficiently prevent damage byelectrostatic discharge and restrain noises.

BACKGROUND ART

In recent years, due to the spread of the Internet and others, theinformation processing amount of personal computers and the processingspeed of information have been required to be increased. Following tothat, it has been requested that the capacity of hard disc drives (HDDs)integrated into personal computers and the speed of informationtransmission are made larger. The type of the component for supporting amagnetic head used in an HDD, which is called a magnetic headsuspension, has also been shifting from a conventional type, to whichsignal lines such as gold wires are connected, to a wiring-integratedtype, i.e., the so-called wireless suspension type, wherein signal linessuch as copper wires are fitted directly to a stainless steel spring.

Recently, demands for HDDs to be mounted into various small-sizeddevices, typical examples of which are portable devices, have beenincreasing. For this reason, the density of HDDs has been made higher,and further the size of magnetic heads has been becoming smaller. Thus,with an increase in the sensitivity of the magnetic heads, the magneticheads are easily affected by electrostatic charging. Accordingly, thereis caused a problem that the properties of small-sized magnetic headelements are changed by electric charges collected in their sliders, andat worst the elements are broken.

Another problem is the following problem: in order to improve the signaltransmission speed and precision of HDDs, there has been a tendency thatelectric signals having a higher frequency are used in recent years; asthe frequency becomes higher, noises of transmitted electric signalsincrease. It has been considered that a cause for generating noises isbased on a difference in potential between the metallic substrate andthe wiring layer.

Against these problems, for example, Patent Document 1 discloses thefollowing matters for preventing a damage of a magnetic head byelectrostatic discharge: the use of an electroconductive resin betweenthe magnetic head and the suspension for the purpose of attainingelectric connection; the formation of an earth electrode on thesuspension side from an electroconductive material such as copper bysputtering, plating, vapor deposition or the like; and others.

For example, Patent Document 2 discloses a method to restrain thegeneration of noises, wherein a ground terminal is set up on a wiredsuspension for attaining a short circuit between wiring and a substratefor the suspension. In the process of forming the ground terminal, anadditive method is used; therefore, required are the step of forming apower-feeding layer through a dry process, and the step of forming awiring layer by electrolytic plating.

According to the above-mentioned prior arts, it is necessary to conducta process for which a relatively long time is required, such assputtering, plating or vapor deposition, when an earth electrode or aground terminal is formed. For this reason, there remain problems thatthe productivity is low and costs increase.

Patent Document 1: Japanese Patent Application publication (JP-A) No.08-111015

Patent Document 2: JP-A No. 2006-12205 DISCLOSURE OF THE INVENTIONProblems to be solved by the invention

In light of the above-mentioned situation, the invention has been made.A main object thereof is to provide a substrate for suspension which isproduced at low costs and can sufficiently attain the prevention ofdamage by electrostatic discharge and restraint of noises.

Means for Solving the Problems

To resolve the above-mentioned problems, the present invention providesa substrate for suspension, comprising: a metallic substrate, aninsulating layer formed on the metallic substrate and having an openingfrom which the metallic substrate is exposed, a grounding-wiring layerformed on the insulating layer and arranged near the opening, and aground terminal formed in the opening and contacting the metallicsubstrate and the grounding-wiring layer, characterized in that theground terminal is made of a metal having a melting point of 450° C. orlower.

According to the invention, the melting point or the liquid phase pointof the metal used to form the ground terminal is relatively low;therefore, the invention has an advantage that the ground terminal caneasily be formed.

In the above-mentioned invention, the ground terminal is preferably aconvex shape having an apex inside a region of the opening in planarview. The thus-shaped ground terminal can be formed by, for example, amethod of dropping the metal, which has a melting point of 450° C. orlower, quantitatively in the state that the metal is melted. This methodmakes it easy to decrease costs or simplify the process.

In the above-mentioned invention, a metal forming the ground terminal ispreferably a lead-free solder. Thereby, the impact of the presentinvention to the environment can be lessening.

In the above-mentioned invention, the grounding-wiring layer ispreferably formed to surround the opening in planar view, and furthercharacterized in that the grounding-wiring layer has an air vent sectionfor restraining an air reservoir generated when the ground terminal isformed. By restraining the generation of the air reservoir, the contactarea between the ground terminal and the metallic substrate can be madesufficiently large.

In the above-mentioned invention, a form of the grounding-wiring layernear the opening is preferably a line form. Thereby, the air reservoiris less likely to be generated.

In the above-mentioned invention, the ground terminal is preferablyformed only inside a region surrounded by an edge of the opening. Thegrounding-wiring layer arranged near the opening can be made small sothat space-saving can be attained and the substrate can be made light.

In the above-mentioned invention, an intermetallic compound layer ispreferably formed in a joint interface between the ground terminal andthe metallic substrate. Electric connection between the ground terminaland the metallic substrate becomes better so that the electricresistance becomes low.

The present invention provides a process for producing a substrate forsuspension, comprising steps of: preparing a substrate-forming memberwhich comprises a metallic substrate, an insulating layer formed on themetallic substrate and having an opening from which the metallicsubstrate is exposed, and a grounding-wiring layer formed on theinsulating layer and arranged near the opening; and aground-terminal-forming step of dropping a metal having a melting pointof 450° C. or lower quantitatively into the opening in a state that themetal is melted, and forming a ground terminal contacting the metallicsubstrate and the grounding-wiring layer.

According to the invention, the melted metal is dropped into the openingso as to form a ground terminal, whereby costs can be decreased and theprocess can be simplified.

In the above-mentioned invention, a dropping method for dropping themetal quantitatively in the state that the metal is melted is preferablya method of using plural metallic balls each having a predetermineddiameter, and melting and dropping the metallic balls successively. Byappropriately selecting the diameter of metallic balls as a feedstock,the drop amount of the melted metal can be freely adjusted.

In the above-mentioned invention, when the metal is dropped in the statethat the metal is melted, the diameter of the melted metal is preferablysmaller than a diameter of the opening. By making the diameter of themelted metal smaller than that of the opening, the melted metal can becaused to hit with a larger certainty.

EFFECTS OF THE INVENTION

The invention produces an advantageous effect of providing a substratefor suspension which is produced at low costs and can sufficientlyattain the prevention of damage by electrostatic discharge and restraintof noises.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plane view illustrating an embodiment of thesubstrate for suspension of the invention.

FIG. 2 is an X-X sectional view of FIG. 1.

FIG. 3 is a schematic sectional view illustrating the shape of a groundterminal formed by plating.

FIGS. 4A and 4B are a schematic sectional view for explaining a groundterminal in the invention.

FIG. 5 is a schematic sectional view for explaining a ground terminal inthe invention.

FIG. 6 is a schematic plane view illustrating another embodiment of thesubstrate for suspension of the invention.

FIG. 7 is a schematic plane view for explaining a grounding-wiring layerused in the invention.

FIG. 8 is a schematic sectional view for explaining an air reservoir.

FIGS. 9A and 9B are a schematic plane view for explaining an air ventsection.

FIGS. 10A and 10B are an explanatory view for explaining agrounding-wiring layer used in the invention.

FIGS. 11A and 11B are a schematic plane view for explaining agrounding-wiring layer used in the invention.

FIGS. 12A to 12C are a schematic sectional view for explaining agrounding-wiring layer used in the invention.

FIG. 13 is a schematic sectional view for explaining the size of agrounding-wiring layer used in the invention.

FIGS. 14A and 14B are a schematic sectional view for explaining acoverlay used in the invention.

FIGS. 15A to 15D are a schematic plane view illustrating the structureof the vicinity of a ground terminal used in the invention.

FIGS. 16A to 16C are a process chart illustrating an embodiment of aprocess for producing the substrate for suspension of the invention.

FIGS. 17A to 17C are a process chart illustrating another embodiment ofa process for producing the substrate for suspension of the invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: metallic substrate    -   2: insulating layer    -   3 a: grounding-wiring layer    -   3 b: writing wiring layer    -   3 c: reading wiring layer    -   4: ground terminal    -   5: opening    -   6: air reservoir    -   7: air vent portion    -   8: coverlay    -   10: substrate-forming member    -   11: dropping device    -   12: melted metal

BEST MODE FOR CARRYING OUT THE INVENTION

The substrate for suspension of the invention, and the productionprocess thereof will be described in detail hereinafter.

A. Substrate for Suspension

First, a substrate for suspension of the present invention will beexplained. The substrate for suspension of the present inventioncomprises: a metallic substrate, an insulating layer formed on themetallic substrate and having an opening from which the metallicsubstrate is exposed, a grounding-wiring layer formed on the insulatinglayer and arranged near the opening, and a ground terminal formed in theopening and contacting the metallic substrate and the grounding-wiringlayer, characterized in that the ground terminal is made of a metalhaving a melting point of 450° C. or lower.

According to the invention, the melting point of the metal used to formthe ground terminal is relatively low; therefore, the invention has anadvantage that the ground terminal can easily be formed. Groundterminals formed by sputtering, vapor deposition, plating or the like inthe prior art are obtained through a process for which a relatively longtime is required. Thus, the ground terminals have problems that theproductivity is low and costs increase. In the invention, however, theground terminal can easily be formed, for example, by dropping a meltedmetal into the opening, as described later.

The following will describe the substrate for suspension of theinvention, using the drawings. FIG. 1 is a schematic plane viewillustrating an embodiment of the substrate for suspension of theinvention, more specifically, an enlarged schematic plane viewillustrating a tip portion thereof on which a magnetic head slider ismounted. The substrate for suspension illustrated in FIG. 1 has astructure wherein a patterned wiring layer (a grounding-wiring layer 3a, a writing wiring layer 3 b and a reading wiring layer 3 c) made of Cuis formed on SUS, which works as a metallic substrate 1 and has a springproperty so as to interpose a polyimide as an insulating layer 2therebetween. Furthermore, the substrate for suspension illustrated inFIG. 1 has a ground terminal 4 for connecting the metallic substrate 1and the grounding-wiring layer 3 a electrically to each other.

FIG. 2 is an X-X sectional view of FIG. 1. As illustrated in FIG. 2, thesubstrate for suspension of the invention has: the metallic substrate 1,the insulating layer 2 formed on the metallic substrate 1 and having anopening 5 from which the metallic substrate 1 is exposed, thegrounding-wiring layer 3 a formed on the insulating layer 2 and arrangednear the opening 5, and the ground terminal 4 formed in the opening 5and contacting the metallic substrate 1 and the grounding-wiring layer 3a. The invention is characterized in that the ground terminal 4 is madeof a metal having a specified melting point.

As illustrated in FIG. 2, in the invention, it is preferred that theground terminal 4 has a convex shape having an apex in the region of theopening 5 in planar view (along the direction A in FIG. 2). Thethus-shaped ground terminal can be formed by, for example, a method ofdropping a melted metal into the opening. This method makes it easy todecrease costs or simplify the process. When a melted metal is droppedinto the opening, the melted metal usually flows after the metal hits,so that a convex shape the apex of which is the spot where the metalhits is formed. In other words, it is preferred that the ground terminalis formed by dropping a metal having a melting point of 450° C. or lowerquantitatively in the state that the metal is melted. In the meantime,when the ground terminal in the invention is formed by plating, theshape of the ground terminal 4 comes to have a concave portion near thecenter of the opening 5, as illustrated in FIG. 3.

The substrate for suspension of the invention will be describedhereinafter in accordance with the individual constituents thereof.

1. Ground Terminal

First, the ground terminal used in the invention is described. Theground terminal used in the invention is a member formed in the opening,which will be described later, and contacting the metallic substrate andthe grounding-wiring layer to have a function of causing the two to beelectrically connected to each other. Furthermore, the ground terminalused in the invention is characterized by being made of a metal having amelting point of 450° C. or lower. It is preferred that the meltingpoint of the metal is 350° C. or lower, in particular, 250° C. or lower.When the melting point of the metal is low, the metal is easily meltedso that the ground terminal can be simply and easily formed.

The “melting point” in the invention refers to a temperature at which amaterial in a solid phase state keeps equilibrium with a liquid phasethereof under a given pressure, and may be called the fusing point. Inthe case of a simple metal, or two or more components having a eutecticcomposition (a mixture of two or more crystals that are simultaneouslycrystallize out a liquid containing two or more components), the meltingpoint is consistent with the freezing point (temperature at which theliquid solidifies) thereof. In the case of a metal which is composed oftwo or more components coexisting while keeping equilibrium and does nothave any eutectic composition, a phase diagram is viewed which shows therelationship between the compositions of the liquid and the solid, whichare composed of the two or more components coexisting while keepingequilibrium, and the temperature, that is, the melting point. In thiscase, the temperature (melting point) is taken on the vertical axisthereof and the composition (ratio between the components) is taken onthe transverse axis thereof, and the temperature at which the liquidphase and the solid phase keep equilibrium is drawn in connection withthe composition of the liquid phase. As a result, a liquidus is gained.The liquid phase point therein is defined as the melting point.

The lower limit of the melting point of the metal is not particularlylimited as far as the limit permits the metal to be in a solid state atnormal temperature (25° C.). The limit is usually 100° C.

The melting point of the metal can be measured by differential thermalanalysis (DTA) or differential scanning calorimetry (DSC) in accordancewith JIS Z3198-1. A thermal analyzer therefor is, for example, DSC 8230or TG 8120 manufactured by Rigaku Corporation.

The metal used in the invention may be a simple metal or an alloy as faras the metal has a melting point of the above-mentioned value or lower.In the invention, the metal is preferably an alloy. When a metal havinga low melting point is mixed, an alloy having a low melting point caneasily be obtained; thus, metals of various kinds can be used.

The alloy is not particularly limited as far as the alloy has a meltingpoint of the above-mentioned value or lower. Specifically, the alloy isan alloy containing at least two selected from the group consisting oftin (Sn), lead (Pb), zinc (Zn), silver (Ag), copper (Cu), indium (In),bismuth (Bi), antimony (Sb), nickel (Ni) and germanium (Ge), or someother alloy. It is preferred in the invention that the alloy is an alloycontaining at least two selected from the group consisting of tin (Sn),lead (Pb), silver (Ag), copper (Cu) and bismuth (Bi).

In the invention, it is also preferred to use, as the alloy, solder.Solder can be roughly classified to lead-containing solder and lead-freesolder. In the invention, lead-containing solder refers to a meltingmaterial made mainly of lead (Pb) and tin (Sn) and having a meltingpoint of the above-mentioned temperature or lower. Lead-free solderrefers to a melting material made mainly of tin (Sn) without containinglead (Pb) and having a melting point of the above-mentioned temperatureor lower. In the invention, it is preferred to use, as the alloy,lead-free solder since loads onto the environment can be decreased.

Specific examples of the above-mentioned lead-free solder include Sn—Sbbased, Sn—Cu-based, Sn—Cu—Ni based, Sn—Ag based, Sn—Ag—Cu based,Sn—Ag—Cu—Bi based, Sn—Zn based, Sn—Ag—In—Bi based, Sn—Zn based, Sn—Bibased, Sn—In based, and Sn—Sb based solders.

Specific examples of the above-mentioned lead-containing solder includeSn—Pb based, Sn—Ag—Pb based, Sn—Pb—Bi based, Sn—Sb—Pb based, andSn—Ag—Sb—Pb based solders.

In the meantime, the simple metal is not particularly limited as far asthe metal has a melting point of the above-mentioned value or lower.Examples thereof include tin (Sn) and lead (Pb).

The shape of the ground terminal is not particularly limited as far asthe shape permits the metallic substrate and the grounding-wiring layerto be electrically connected to each other. The shape of the groundterminal is varied in accordance with the shape of the opening, whichwill be described later, and other factors.

The resistance value of the ground terminal is not particularly limited,and is preferably, for example, 5Ω or less, more preferably 1Ω or less,in particular preferably 0.5Ω or less.

In the case of melting a low-melting-point metal and dropping the metalin an opening in an insulating layer, thereby forming the groundterminal, it is allowable in the invention to conduct flux treatment inorder to remove a metal oxide film formed on the surface of the metal,such as SUS. Such flux treatment is a treatment which is not conductedin the case of forming a ground terminal by plating or the like.Therefore, when it is checked whether or not a residue of the flux ispresent, it is possible to judge whether or not the ground terminal isproduced by plating or the like. Whether or not the flux residue ispresent can be checked by ion chromatography, AES (atomic emissionspectroscopy) and XPS (X-ray photoelectron spectroscopy).

It is also preferred in the invention that the ground terminal is formedonly inside a region surrounded by the edge of the opening. This makesit possible to make the grounding-wiring layer arranged near the openingsmall, and attain space-saving and a reduction in the weight. When thevicinity of the ground terminal can be made light, the metallicsubstrate can also be made thin.

As illustrated in FIG. 4A, a specific example thereof is a substrate forsuspension wherein the ground terminal 4 is formed only inside a regionsurrounded by an edge B of the opening 5. As illustrated in FIG. 4B, inthe invention, allowable is a substrate for suspension wherein thegrounding-wiring layer 3 a has a smaller opening than the opening 5. Inorder to improve the joint reliability, it is preferred that the groundterminal is formed to be filled into the opening. In the meantime, inorder to make the substrate light, the ground terminal may be formed notto be filled into a part of the opening.

An example of the method for forming the ground terminal includes amethod, wherein when a metal is dropped into the opening in the statethat the metal is melted, the diameter of the melted metal is madesmaller than that of the opening, as will be described in “B. Processfor producing a substrate for suspension”, which is located later.

It is also preferred in the invention that an intermetallic compoundlayer is formed in a joint interface between the ground terminal and themetallic substrate. This makes it possible to make electric connectionbetween the ground terminal and the metallic substrate better so thatthe electric resistance becomes low. As illustrated in FIG. 5, aspecific example thereof includes a substrate for suspension wherein anintermetallic compound layer 21 is formed in a joint interface betweenthe ground terminal 4 and the metallic substrate 1.

The intermetallic compound layer usually has both components of themetal constituting the ground terminal and the metal constituting themetallic substrate. For example, in the case of using Cu or Au as themetal constituting the ground terminal and using SUS 304 as the metallicsubstrate, the intermetallic compound layer has a Cu element, a Auelement, a Sn element, and so on.

About the composition of the intermetallic compound layer, a crosssection thereof can be measured by, for example, EDX or AES.

The film thickness of the intermetallic compound layer is notparticularly limited as far as the thickness permits electricconnectivity between the ground terminal and the metallic substrate tobe improved. The film thickness is preferably in the range of, forexample, 0.1 μm to 5.0 μm, in particular preferably in the range of 1.0μm to 3.0 μm.

An example of the method for forming the intermetallic compound layerincludes a method of removing the oxide film from the exposed metallicsubstrate, and then bringing the melted metal and the exposed metallicsubstrate into contact with each other before a metal oxide film isformed on the surface of the metallic substrate after the metallicsubstrate being washed, as will be described in “B. Process forproducing a substrate for suspension”, which is located later.

2. Insulating Layer and Grounding-Wiring Layer

Next, the insulating layer and the grounding-wiring layer used in theinvention are described. The insulating layer used in the invention is alayer formed over the metallic substrate and having an opening fromwhich the metallic substrate is exposed. The grounding-wiring layer usedin the invention is a layer formed on the insulating layer and arrangednear the opening.

The insulating layer used in the invention has an opening from which themetallic substrate is exposed at a position where the ground terminal isto be formed. The shape of the opening is not particularly limited asfar as the shape permits the ground terminal to cause the metallicsubstrate and the grounding-wiring layer to be electrically connected toeach other. The shape is, for example, a circle; an ellipse; any polygonsuch as a rectangle or a pentagon; a comb-shape; a cross shape; or a rodshape. The shape of the opening is generally a circle. When the shape ofthe opening is a circle, the diameter thereof is usually from about 50μm to 300 μm.

The position of the opening is not particularly limited, and thus theopening may be made in any position as far as the position is a positionpermitting the ground terminal to cause the metallic substrate and thegrounding-wiring layer to be electrically connected to each other. Forexample, as illustrated in FIG. 1, the opening may be made at the tipportion of the substrate for suspension, on which a magnetic head slideris mounted. As illustrated in FIG. 6, the opening may be made in aportion other than the tip portion of the substrate for suspension. InFIG. 6, the grounding-wiring layer 3 a is formed between the writingwiring layer 3 b and the reading wiring layer 3 c, and the opening 5 ismade inside a region of the insulating layer 2 where thegrounding-wiring layer 3 a is formed.

In the meantime, the grounding-wiring layer used in the invention isformed on the insulating layer and further arranged near the opening. Inthe invention, the grounding-wiring layer and the metallic substrate areelectrically connected to each other through the ground terminal. Thewording “near the opening” refers to locations where the layer can besubstantially grounded to the opening through the ground terminal. Thelocations refer to, for example, a region from the edge of the openingto points 50 μm apart therefrom.

The shape of the grounding-wiring layer is not particularly limited andmay be set to any shape as far as the shape permits the layer to beelectrically connected to the metallic substrate through the groundterminal. Usually, the grounding-wiring layer is formed to surround theopening in planar view. Specifically, as illustrated in FIG. 7, thegrounding-wiring layer 3 a is formed to surround the opening 5 formed inthe insulating layer 2 in planar view.

In a case where the grounding-wiring layer is formed to surround theopening in planar view as described above and further, as will bedescribed later, the ground terminal is formed by melting alow-melting-point metal and dropping the metal in the opening, a spaceinto which air is discharged is lost at the time of the dropping, sothat an air reservoir is generated. As a result, contact between theground terminal and the metallic substrate may become insufficient.Specifically, as illustrated in FIG. 8, an air reservoir 6 is generatedso that contact between the ground terminal 4 and the metallic substrate1 may become insufficient.

In a case as described above, therefore, it is preferred that at leastone of the grounding-wiring layer and the insulating layer has an airvent section for restraining an air reservoir generated when the groundterminal is formed. The restraint of the generation of the air reservoirmakes it possible to make the contact area between the ground terminaland the metallic substrate sufficiently large. An example of thegrounding-wiring layer having the air vent section includes thegrounding-wiring layer 3 a having an air vent section 7 as illustratedin FIG. 9A. Similarly, both of the grounding-wiring layer 3 a and theinsulating layer 2 may have air vent sections 7 (FIG. 9B). Only theinsulating layer may have an air vent section (not illustrated). In acase where the grounding-wiring layer is made of copper, an air ventsection having a size of about 20 μm to 50 μm may be formed. Thegrounding-wiring layer or the insulating layer may have plural air ventsections.

In the invention, the grounding-wiring layer may not be formed tosurround the opening in planar view. Specifically, as illustrated inFIG. 10A, the grounding-wiring layer 3 a may be formed merely near theopening 5. In other words, the form of the grounding-wiring layer nearthe opening may be a line form. As illustrated in FIG. 10B, in such acase also, the ground terminal 4 can sufficiently cause thegrounding-wiring layer 3 a and the metallic substrate 1 to beelectrically connected to each other. In this case, it is unnecessary toprovide the air vent section to the grounding-wiring layer or theinsulating layer. As illustrated in FIG. 11A, plural line-formgrounding-wiring layers 3 a may be formed near the opening 5. This makesit possible to improve the joint reliability. As illustrated in FIG.11B, a line-form grounding-wiring layer 3 a may be formed so as tocontact the opening 5 when they are viewed in plane view. This makes itpossible to improve the design-flexibility in the position of theopening.

As illustrated in FIG. 12A, in the invention, the grounding-wiring layer3 a may have a smaller opening than the opening 5. As illustrated inFIG. 12B, the grounding-wiring layer 3 a may have an opening the size ofwhich is equal to that of the opening 5. As illustrated in FIG. 12C, thegrounding-wiring layer 3 a may have a larger opening than the opening 5.

As will be described later, in the invention, a metal having a meltingpoint of 450° C. or lower is quantitatively dropped into the opening inthe state that the metal is melted, whereby the ground terminalcontacting the metallic substrate and the grounding-wiring layer can beformed (see FIGS. 16A to 16C, which will be referred to later). In thiscase, the grounding-wiring layer can be made smaller than inconventional methods for forming a ground terminal, such as plating. Asa result, space-saving and a reduction in the weight can be attained. Inorder to prevent deterioration in the insulating layer, it is preferredto form the grounding-wiring layer in such a manner that the groundterminal and the insulating layer do not contact each other. Asillustrated in FIG. 13, the distance between the edge of the opening 5and an end of the grounding-wiring layer 3 a, the end being farther fromthe opening 5, is determined as the distance C. When the above-mentionedmethod is used to form the ground terminal in the invention, thegrounding-wiring layer can be made smaller than the case of plating orthe like in the prior art is used. In this case, the distance C can beset to 75 μm or less, in particular, 50 μm or less.

As will be described later, it is preferred in the invention that at thetime of dropping a metal into the opening in the state that the metal ismelted, the diameter of the melted metal is made smaller than that ofthe opening (see FIGS. 17A to 17C, which will be referred to later).This makes it possible to make the grounding-wiring layer arranged nearthe opening even smaller. In this case, the distance C may be set to 40μm or less, in particular, 30 μm or less. In order to keep themechanical strength of the grounding-wiring layer certainly, thedistance C is usually 20 μm or more.

The thickness of the insulating layer is not particularly limited as faras the thickness permits the layer to exhibit desired insulatingproperties. The thickness is usually from about 5 μm to 10 μm. Thethickness of the grounding-wiring layer is not particularly limited asfar as the thickness permits the layer to exhibit a desiredelectroconductivity. The thickness is usually from about 6 μm to 18 μm.

The material of the insulating layer is, for example, polyimide (PI).The material of the grounding-wiring layer is, for example, copper (Cu).Furthermore, the grounding-wiring layer may be plated with nickel (Ni)or gold (Au). When the layer is plated with, in particular, gold (Au),the bondability between the solder and the grounding-wiring layer isimproved; however, if the thickness of the gold plating is large,brittle Au of the plating and Sn of the solder diffuse mutually in thebonding interface between Au and the solder, so that a very brittleintermetallic compound of Au—Sn is generated or Kirkendal voids aregenerated by a difference in diffusion speed between the two metals. Asa result, the bonding state may become instable. Thus, the thickness ofthe gold plating is preferably 0.5 μm or less, more preferably fromabout 0.1 μm to 0.2 μm.

3. Metallic Substrate

Next, the metallic substrate used in the invention is described. Themetallic substrate used in the invention is not particularly limited asfar as the metallic substrate has electroconductivity. Since thesubstrate for suspension of the invention is used for a suspension, themetallic substrate usually has an appropriate spring property.

It is preferred in the invention that the metallic substrate has anelectroconductive layer on the front surface side thereof, wherein theopening is formed. The formation of the electroconductive layer makes itpossible to make electric connection through the ground terminal moreeffective. The material of the electroconductive layer is specificallycopper (Cu) or the like. The electroconductive layer may be formed by,for example, plating.

The thickness of the metallic substrate is varied in accordance with thematerial of the metallic substrate, and others, and is not particularlylimited. The thickness usually ranges from 5 μm to 20 μm. The materialof the metallic substrate is, for example, SUS.

4. Others

The substrate for suspension of the invention has at least theabove-mentioned metallic substrate, insulating layer, which has anopening, grounding-wiring layer, and ground terminal. Furthermore, thesubstrate for suspension of the invention usually has a coverlay (CL) onthe grounding-wiring layer. As illustrated in FIG. 14A, in theinvention, a coverlay 8 may be formed to cover a part of thegrounding-wiring layer 3 a. As illustrated in FIG. 14B, a coverlay 8 maybe formed not to cover the grounding-wiring layer 3 a. The former fallswithin the so-called SMD (solder mask defined), and the latter fallswithin the so-called NSMD (non-solder mask defined). The thickness ofthe coverlay is not particularly limited, and is usually from 5 μm to 30μm, in particular preferably from 5 μm to 15 μm. The material of thecoverlay is not particularly limited, and may be equivalent to that of acoverlay used in an ordinary flexible substrate or the like.

FIGS. 15A to 15D illustrate schematic plane views illustratingembodiments of the structure of the vicinity of a ground terminal in theinvention. FIG. 15A illustrates an NSMD type ground terminal 4, whereina coverlay 8 does not cover a grounding-wiring layer 3 a, and the groundterminal 4 is formed along an opening in the grounding-wiring layer 3 a.FIG. 15B illustrates an SMD type ground terminal 4, wherein a coverlay(coverlay for grounding-wiring layer) 8 covers a part of agrounding-wiring layer 3 a, and the present structure has an air ventsection 7, the coverlay 8 for grounding-wiring layer, and a coverlay 8′for insulating layer. In this case, the ground terminal 4 is formedalong an opening in the coverlay 8 for grounding-wiring layer. FIG. 15Cillustrates an SMD type ground terminal 4, wherein a coverlay 8 covers apart of a grounding-wiring layer 3 a, and this layer 3 a is in a lineform. In this case, the ground terminal 4 is formed along an opening inthe coverlay 8. FIG. 15D illustrates an NSMD type ground terminal 4,wherein a coverlay 8 does not cover a part of a grounding-wiring layer 3a, and the present structure has an air vent section 7. In this case,the ground terminal 4 is formed along an opening in the grounding-wiringlayer 3 a.

The substrate for suspension of the invention usually has a writingwiring layer and a reading wiring layer besides the grounding-wiringlayer explained above. The writing wiring layer and the reading wiringlayer may be made of the same material of which the grounding-wiringlayer is made, and may be made of a material different from the materialof the grounding-wiring layer. Usually, the layers are made of the samematerial. This makes it possible to decrease costs.

The article for which the substrate for suspension of the invention isused is not particularly limited, and is, for example, a magnetic headsuspension of a hard disc drive (HDD).

B. Process for Producing a Substrate for Suspension

Next, a process for producing a substrate for suspension of the presentinvention will be explained. The process for producing a substrate forsuspension of the present invention comprises steps of: preparing asubstrate-forming member which comprises a metallic substrate, aninsulating layer formed on the metallic substrate and having an openingfrom which the metallic substrate is exposed, and a grounding-wiringlayer formed on the insulating layer and arranged near the opening; anda ground-terminal-forming step of dropping a metal having a meltingpoint of 450° C. or lower quantitatively into the opening in a statethat the metal is melted, and forming a ground terminal contacting themetallic substrate and the grounding-wiring layer.

According to the invention, the melted metal is dropped into the openingso as to form a ground terminal, whereby costs can be decreased and theprocess can be simplified. For example, in the case of forming a groundterminal by plating in the prior art, many steps are required, examplesof which include the step of laminating a dry film; the step of exposingthe dry film to light; the step of developing the exposed dry film; thestep of removing an oxide film on the surface of SUS for an openingwherein the ground terminal is to be formed; the step of plating theinside of the opening; and the step of peeling off the dry film.Furthermore, in order to plate the inside of the opening, which is veryfine, many other regions need to be masked. This is a very inefficientwork. On the other hand, in the invention, a ground terminal can beformed only through the step of dropping a melted metal and an optionalstep of subjecting a metallic substrate to pre-treatment. Thus, costscan be reduced and the process can be made simple.

In the invention, heating is essential for melting the metal; however,it is unnecessary in principle to heat a substrate for suspension(substrate-forming member) before a ground terminal is formed. It istherefore possible to prevent, for example, polyimide, which is used foran insulating layer, from deteriorating. For example, when a groundterminal is formed by plating in the prior art, the resultant groundterminal is brittle so that the terminal may not have a sufficientstrength in a case where the shape of the opening is complicated. On theother hand, in the invention, the metal is dropped in the state that themetal is melted; therefore, the invention has an advantage that it neverhappens that the resultant ground terminal is brittle unlike the case ofplating. Moreover, according to the invention, a ground terminal can beformed in an opening having any shape.

The following will describe the process for producing a substrate forsuspension of the invention, using the drawings. FIGS. 16A to 16C areprocess charts illustrating an embodiment of the process for producing asubstrate for suspension of the invention. The process illustrated inFIGS. 16A to 16C, for producing a substrate for suspension, has: aprocess of preparing a substrate-forming member 10 having a metallicsubstrate 1, an insulating layer 2 formed on the metallic substrate 1and having an opening 5 from which the metallic substrate 1 is exposed,and a grounding-wiring layer 3 a formed on the insulating layer 2 andarranged near the opening 5 (FIG. 16A); and a ground-terminal-formingstep of using a dropping device 11 to drop a melted metal 12quantitatively into the opening 5 (FIG. 16B), thereby forming a groundterminal 4 contacting the metallic substrate 1 and the grounding-wiringlayer 3 a (FIG. 16C).

1. Ground-Terminal-Forming Step

First, the ground-terminal-forming step in the invention is described.In the ground-terminal-forming step in the invention, theabove-mentioned substrate-forming member is used. This substrate-formingmember is a member having at least a metallic substrate, an insulatinglayer having an opening, a grounding-wiring layer, and a groundterminal. About these constituting members, the contents thereof are thesame as described in the item “A. Substrate for suspension”; thus,description thereof is omitted herein. In the present step, a metalhaving a melting point in a specified range is used. About this metalalso, the content thereof is the same as described the item “A.Substrate for suspension”; thus, description thereof is omitted herein.

The dropping method for dropping the metal in the state that the metalis melted is not particularly limited as far as the method is a methodcapable of dropping the melted metal quantitatively. Examples thereofinclude a method of using metallic balls having a predetermined diameterand melting and dropping the metallic balls successively, and a methodof storing a metal in a predetermined container in the state that themetal is melted, and quantitatively dropping the metal bit by bit fromthe container.

In the invention, the dropping method is preferably the method of usingmetallic balls having a predetermined diameter and melting and droppingthe metallic balls successively. By selecting the diameter of metallicballs as a feedstock appropriately, the drop amount of the melted metalcan be adjusted at will. The diameter of the metallic balls is notparticularly limited, and is usually from about 100 μm to 200 μm. In theinvention, it is preferred to decide the diameter of the metallic balls,considering the size of the opening, and others.

The dropping device wherein the metallic balls are used to attain thedropping is, for example, a device having a feedstock supplying unit forsupplying the metallic balls, a melting unit for melting the suppliedmetallic balls, and a dropping unit for dropping the metallic balls. Insuch a device, the metallic balls as a feedstock are first filled intothe feedstock supplying unit, and then the metallic balls aresuccessively supplied from the feedstock supplying unit to the meltingunit to melt the supplied metallic balls. The manner for melting theballs is, for example, a YAG laser. Thereafter, the melted metallicballs are dropped from the dropping unit to the opening. The manner fordropping the melted metallic balls is, for example, a manner ofextruding the melted metallic balls by effect of an inert gas such asN₂. Specific examples of such a dropping device include SB²-JETmanufactured by PAC-TECH PACKAGING TECHNOLOGIES Gmbh.

In the invention, it is allowable that the melted metal is dropped onceor is separately dropped plural times into a predetermined amountnecessary for forming the ground terminal. The case where the metal isdropped once has an advantage that the number of steps is reduced, andthe case where the metal is separately dropped plural times has anadvantage that the generation of an air reservoir can be restrained bydropping the metal bit by bit. In other words, the case where the metalis separately dropped plural times has an advantage that the air ventsection described in the item “A. Substrate for suspension” may not beset up to the grounding-wiring layer or the insulating layer.

It is also preferred in the invention that when the metal is dropped ina metal-melted state, the diameter of the melted metal is set in such amanner that the metal is not brought into contact with the edge of theopening. Specifically, it is preferred that when the metal is dropped ina metal-melted state, the diameter of the melted metal is smaller thanthat of the opening. By making the diameter of the melted metal smallerthan that of the opening, the melted metal can be hit with a largercertainty. According to this, the generation of an air reservoir can berestrained so that the joint area between the metallic substrate and theground terminal increases. As a result, the joint reliability isimproved. Furthermore, the precision of the hit is improved, therebymaking it possible to make the grounding-wiring layer arranged near theopening small. Thus, space-saving can be attained and the weight can besmall. When the vicinity of the ground terminal can be made light, themetallic substrate can also be made thin.

Specifically, as illustrated in FIG. 17A, at the time of using adropping device 11 to drop a melted metal 12 into an opening 5, thediameter 12 x in the horizontal direction of the melted metal 12 is madesmaller than the diameter of the opening 5. As illustrated in FIG. 17B,according to this way, the melted metal 12 is easily hit onto thesurface of a metallic substrate 1 exposed from the opening 5. Asillustrated in FIG. 17C, the resultant ground terminal 4 is formed onlyinside a region surrounded by the edge of the opening 5. About theresultant ground terminal, the content thereof is the same as describedin the item “A. Substrate for suspension”. Thus, description thereof isomitted herein.

The diameter of the melted metal in the invention refers to the size(reference numerals 12 x in FIG. 17A) in the horizontal direction of themelted metal dropped from the dropping device or the like when the metalenters the opening. The diameter of the opening is varied in accordancewith the shape of the opening; in a case where the shape of the openingis, for example, a circle, the diameter refers to the diameter of thecircle. In the invention, the diameter of the melted metal (actually,only the size of the solder balls is clearly specified before the ballsare melted, and the diameter of the metal while the metal is meltedcannot be measured) is smaller than the diameter of the openingpreferably by, for example, 10 μm or more, more preferably by a valueranging from 15 μm to 30 μm.

As illustrated in, for example, FIG. 16A, in a case where the diameterof the grounding-wiring layer 3 a is smaller than that of the opening 5,it is preferred that the diameter of the melted metal is smaller thanthat of the grounding-wiring layer by a value in the above-mentionedrange.

If the diameter of the melted metal is too small, the formed groundterminal may not be able to attain a sufficient connection between themetallic substrate and the grounding-wiring layer. Therefore, in a casewhere the ground terminal is formed by dropping the metal once, it ispreferred to set the diameter of the melted metal into such an extentthat the metallic substrate and the grounding-wiring layer can besufficiently connected to each other. It is preferred to consider therelationship between the volume of the melted metal and the area of theopening at this time. Even if the diameter of the melted metal is toosmall, a sufficient connection between the metallic substrate and thegrounding-wiring layer can be attained by dropping the metal pluraltimes as described above.

The diameter of the melted metal is not particularly limited, and rangesusually from 40 μm to 150 μm, preferably from 60 μm to 100 μm. Thediameter of the opening is usually from about 50 μm to 300 μm, asdescribed in the item “A. Substrate for suspension”. When the diameterof the melted metal is smaller than that of the opening, the diameter ofthe opening is preferably set into, for example, the range of 80 μm to150 μm.

It is also preferred in the invention to subject the metallic substrateexposed from the opening to oxide-film-removing treatment, andsubsequently bring the melted metal and the exposed metallic substrateinto contact with each other before a metal oxide film is formed on thesurface of the metallic substrate after the metallic substrate beingwashed. When a ground terminal is formed before the metal oxide film isformed, a ground terminal low in resistance can be obtained. Moreover, aflux-coating step and a flux-washing step are unnecessary, which isdifferent from a method using a flux, which will be described later.Thus, the process can be made simple. Furthermore, in the case of usinga flux, the flux scatters and simultaneously the ground terminal mayalso scatter when the melted metal is dropped. On the other hand, theoxide-film-removing treatment does not result in a problem offlux-scattering and others, and makes it possible to prevent the groundterminal from scattering.

In general, by applying oxide-film-removing treatment to the metallicsubstrate, a metal oxide film present on the surface of the metallicsubstrate can be removed. However, when the metallic substrate isallowed to stand still in the atmosphere after the oxide-film-removingtreatment, a metal oxide film may again be formed on the metallicsubstrate surface. This metal oxide film is a component making theresistance of the ground terminal high; therefore, it is preferred toform the ground terminal before the metal oxide film is formed.

In the invention, the wording “before a metal oxide film is formed onthe surface of the metallic substrate” refers to a state that a metaloxide film is not formed to such an extent that the ground terminal canexhibit a target resistance value. The target resistance value is variedin accordance with the usage of the substrate for suspension, and otherfactors. For example, the value is preferably 1.0Ω or less, inparticular, 0.3Ω or less.

When the ground terminal is formed before the metal oxide film isformed, it appears that an intermetallic compound layer is formed in ajoint interface between the ground terminal and the metallic substrate.About the intermetallic compound layer, the content thereof is the sameas described in the item “A. Substrate for suspension”. Thus,description thereof is omitted herein. It is also preferred in theinvention to bring the melted metal and the exposed metallic substrateinto contact with each other in an intermetallic-compound-layer formableperiod, which is a period when the intermetallic compound layer can beformed in the joint interface between the ground terminal and themetallic substrate, after the oxide-film-removing treatment is appliedto the metallic substrate exposed from the opening.

When SUS 304 is used for the metallic substrate in the invention, ameasurement of the composition of elements in a SUS 304 surfacedemonstrates that the element composition ratio of Fe/Cr is less than 1before the oxide-film-removing treatment. This would be because achromium oxide film is formed on the SUS 304 surface. When SUS 304 issubjected to the oxide-film-removing treatment, the chromium oxide filmon the SUS 304 surface is removed so that the element composition ratioof Fe/Cr tends to increase.

It is allowable in the invention that metallic balls as a feedstock arebeforehand arranged in the opening and the metallic balls are melted,thereby forming a ground terminal. This process is a process similar tothe so-called SBB (solder ball bonding).

2. Other Steps

Before the melted metal is dropped into the opening, thesubstrate-forming member may be subjected to pre-treatment in theinvention. Specific examples of the pre-treatment include: a fluxtreatment step for removing the metal oxide film on the metallicsubstrate surface exposed from the opening, an acid washing step forremoving the metal oxide film on the metallic substrate surface exposedfrom the opening, a plasma washing step for removing organic substancesremaining on the metallic substrate surface exposed from the opening,and a degreasing step for removing oil components remaining on themetallic substrate surface exposed from the opening. It is particularlypreferred in the invention to conduct the plasma washing step as thepre-treatment step. In the invention, two or more of the above-mentionedpre-treatments may be combined.

The flux agent used in the flux treatment step is not particularlylimited. Preferably, the agent is appropriately selected in accordancewith the kind of the metallic substrate. The flux agent may beequivalent to a flux agent used for ordinary solder or the like.

In the plasma washing step, the oxide film on the metallic substrate isremoved at the same time when organic residues on the metallic substrateare removed. The gas selected for the treatment is He alone, N₂ alone,Ar alone, or a mixed gas containing hydrogen in an amount of 3% or less.The plasma machine is preferably of a high energy-efficiency type, suchas a parallel plate type, or a magnetron type.

Examples of the acid washing solution used in the acid washing stepinclude hydrochloric acid, sulfuric acid, hydrogen peroxide, phosphoricacid, and acidic ammonium fluoride. These may be used alone or in theform of a mixture.

The degreasing method used in the degreasing step is not particularlylimited, and examples thereof include alkali degreasing using sodiumcarbonate, sodium hydroxide or the like; emulsion degreasing; solventdegreasing; acidic degreasing using phosphoric acid, a silicate or thelike; and degreasing using a surfactant, a chelating agent or the like.These may be used alone or in combination of two or more thereof.

The invention is not limited to above-mentioned embodiments. Theembodiments are exemplified, and any embodiment having substantially thesame structure as the technical concept recited in the claims of theinvention and producing the same effects and advantages is included inthe technical scope of the invention.

EXAMPLES

The invention will be more specifically described by way of thefollowing examples.

Example 1 Formation of a Substrate-Forming Member

Prepared was a laminate wherein an SUS 304 of 20 μm thickness (metallicsubstrate), a polyimide layer of 10 μm thickness (insulating layer), anda Cu wiring layer of 18 μm thickness (wiring layer) made of electrolyticcopper foil were laminated in this order. This laminate was subjected tochemical etching and other treatments described below, thereby yieldinga substrate-forming member. First, a region of the Cu wiring layer wherea ground terminal was to be formed (grounding Cu wiring layer) wasworked into a shape having an outer diameter of 250 μm and an innerdiameter (opening diameter) of 100 μm by chemical etching. Next, the SUSwas chemically etched in order to specify the external shape of asubstrate for suspension. Next, the polyimide layer was chemicallyetched to make an opening having a diameter of 100 μm. Thereafter, thesurface of the grounding Cu wiring layer was plated with Ni up to athickness of about 0.2 μm by electroplating, and then plated with Au upto a thickness of about 0.5 μm by electroplating. Furthermore, aphotosensitive coverlay coating for wiring-protection was coated ontothe resultant. The resultant was exposed to light and developed to forma coverlay having a predetermined shape. In this way, asubstrate-forming member was yielded.

(Formation of Substrates for Suspension)

Next, in order to activate the SUS surface in the opening, treatmentusing phosphoric acid (acid washing) was conducted as pre-treatment.Thereafter, lead-free solders (solder balls) having a diameter of 0.1 mmand made of Sn-3.0Ag-0.5Cu were prepared, and an SB²-JET manufactured byPac-Tech PACKAGING TECHNOLOGIES Gmbh was used to drop the solder ballsinto the opening while the balls were melted. In such a way, substratesfor suspension of the invention were yielded. The average of theresistance values of the ground terminals of these substrates forsuspension was 6.10Ω. The ratio of substrates having a resistance of 5Ωor less out of the substrates was 40%, and the ratio of substrateshaving a resistance of 1Ω or less was 5%.

Example 2

Substrates for suspension were yielded in the same way as in Example 1except that instead of the acid washing, a treatment with Ar gas wasconducted in a parallel plate type plasma washing machine manufacturedby March Plasma Systems, Inc. for 5 minutes before the melted solder wasdropped, so as to activate the SUS surfaces. The average of theresistance values of the ground terminals of these substrates forsuspension was 1.25Ω. The ratio of substrates having a resistance of 5Ωor less out of the substrates was 90%, and the ratio of substrateshaving a resistance of 1Ω or less was 65%.

Example 3

Substrates for suspension were yielded in the same way as in Example 1except that instead of the acid washing, a flux (NS-23, manufactured byNihon Superior Co., Ltd.) for SUS was coated before the melted solderwas dropped, so as to activate the SUS surfaces. The average of theresistance values of the ground terminals of these substrates forsuspension was 5.55Ω. The ratio of substrates having a resistance of 5Ωor less out of the substrates was 60%, and the ratio of substrateshaving a resistance of 1Ω or less was 5%.

Example 4

First, the same substrate-forming member as in Example 1 was prepared(opening diameter: 100 μm). Next, lead-free solders (solder balls)having a diameter of 0.1 mm and made of Sn-3.0Ag-0.5Cu were prepared,and then an SB²-JET manufactured by Pac-Tech PACKAGING TECHNOLOGIES Gmbhwas used to drop the melted solder balls into the opening in the statethat the diameter in the horizontal direction of the melted balls wasadjusted to 80 μm. In this way, a ground terminal was formed.

1. A substrate for suspension, comprising: a metallic substrate, aninsulating layer formed on the metallic substrate and having an openingfrom which the metallic substrate is exposed, a grounding-wiring layerformed on the insulating layer and arranged near the opening, and aground terminal formed in the opening and contacting the metallicsubstrate and the grounding-wiring layer, wherein the ground terminal ismade of a metal having a melting point of 450° C. or lower.
 2. Thesubstrate for suspension according to claim 1, wherein the groundterminal is a convex shape having an apex inside a region of the openingin planar view.
 3. The substrate for suspension according to claim 1,wherein a metal forming the ground terminal is a lead-free solder. 4.The substrate for suspension according to claim 1, wherein thegrounding-wiring layer is formed to surround the opening in planar view,and further wherein the grounding-wiring layer has an air vent sectionfor restraining an air reservoir generated when the ground terminal isformed.
 5. The substrate for suspension according to claim 1, wherein aform of the grounding-wiring layer near the opening is a line form. 6.The substrate for suspension according to claim 1, wherein the groundterminal is formed only inside a region surrounded by an edge of theopening.
 7. The substrate for suspension according to claim 1, whereinan intermetallic compound layer is formed in a joint interface betweenthe ground terminal and the metallic substrate.
 8. A process forproducing a substrate for suspension, comprising steps of: preparing asubstrate-forming member which comprises a metallic substrate, aninsulating layer formed on the metallic substrate and having an openingfrom which the metallic substrate is exposed, and a grounding-wiringlayer formed on the insulating layer and arranged near the opening; anda ground-terminal-forming step of dropping a metal having a meltingpoint of 450° C. or lower quantitatively into the opening in a statethat the metal is melted, and forming a ground terminal contacting themetallic substrate and the grounding-wiring layer.
 9. The process forproducing a substrate for suspension according to claim 8, wherein adropping method for dropping the metal quantitatively in the state thatthe metal is melted is a method of using plural metallic balls eachhaving a predetermined diameter, and melting and dropping the metallicballs successively.
 10. The process for producing a substrate forsuspension according to claim 8, wherein when the metal is dropped inthe state that the metal is melted, a diameter of the melted metal issmaller than a diameter of the opening.
 11. The process for producing asubstrate for suspension according to claim 9, wherein when the metal isdropped in the state that the metal is melted, the diameter of themelted metal is smaller than a diameter of the opening.